The present invention relates generally to outer air seals for gas turbine engines, such as aircraft jet engines, and more specifically to an improved structure for supplying cooling air to the back of outer air seals.
Outer air seals closely surround the outside of an imaginary hoop traced by the moving tips of spinning rotor blades in gas turbine engines. They block, as much as possible, any flow of turbine combustion gases over the blade tips to confine the flow of combustion gas to an intended annular flowpath past the blade lengths.
The seals are divided into many arcuate segments to allow for differential thermal expansion between the seals and their supporting structures, which supporting structures are in turn attached to the engine case structure. Because the seals are in contact with the hot, pressurized combustion gases, they must be cooled to keep their temperature within acceptable limits and to provide an adequate service life.
The prior art includes a number of minor variations on a conventional structure for cooling outer air seals. As disclosed in U.S. Pat. No. 4,642,024 to Weidner, conventional outer air seals include the seal surface, which faces the blade tips and is generally a ceramic, attached to a substrate which generally comprises a backplate having on its back flange hooks which engage a boxlike support structure that is in turn attached to the engine case structure. Cooling air is flowed into the cavity formed by the engine case structure, the sides of the support structure and the backplate. A perforated cooling impingement plate is mounted in a spaced relationship over the backplate to redirect cooling air into jets which perpendicularly impact the backplate to increase cooling over that which would result if the cooling air merely passed over the backplate.
The interlocking arrangement of the various rigid outer air seal components, particularly where the outer air seal attaches to the engine case structure, creates a large number of unwanted leak paths for the cooling air. The prior art has in some cases addressed this problem by directing the unavoidably leaking air to other structural components where cooling may be of value. This has not, of course, provided a complete solution. Thus it is seen that there is a need for an improved outer air seal that avoids the leaks inherent in the prior art.
It is, therefore, a principal object of the present invention to provide an outer air seal assembly that has a leakproof connection for cooling air between the seal assembly and the engine case structure.
It is a feature of the present invention that it includes a manifold that more directly flows cooling air toward the holes in the impingement plate than the more generalized flow in the prior art.
It is an advantage of the present invention that it provides much more precise control over the cooling air after impinging on the backplate.
It is another advantage of the present invention that its implementation is straightforward and uncomplicated.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.